RF-ultrasound relay for efficient power and data transfer across interfaces

ABSTRACT

A hybrid RF-acoustic relay is provided where some but not all of the incident RF power is rectified to power the relay and, optionally, to provide power for further link features. The remaining fraction of the incident RF power is used to directly drive an acoustic transceiver array in communication with one or more acoustically powered nodes. In this manner, power, control and communication can be efficiently provided to acoustically powered nodes even in situations where an RF link or an acoustic link would perform poorly.

FIELD OF THE INVENTION

This invention relates to hybrid RF-acoustic links for providing power(and optionally data communication) to acoustic devices.

BACKGROUND

Acoustically powered devices are under consideration for variousapplications, including medical implants. One challenge for suchimplants is providing power to them, because it is often challenging toacoustically transmit power to an acoustically powered implant.Achieving a good acoustic contact with skin of a user can be a burden onthe user, and the acoustic power may need to pass through body partshaving high acoustic attenuation to reach the implant. For example, anacoustically powered retinal implant would face significant designdifficulties because of high acoustic attenuation from bone in the skullthrough which the acoustic energy would need to travel when powering isdone from the side of the head.

Such considerations have motivated the investigation of hybridRF-acoustic links, where part of the link is electromagnetic (i.e. RF)and the other part of the link is acoustic. For example, a hybridRF-acoustic link to acoustic nodes in the brain of a patient could use arelay positioned under the skull of the patient. Such a relay would bein acoustic communication with the implants in the brain, and also be inRF communication with an external unit. In this approach, transmissionthrough the skull is RF, not acoustic, thereby avoiding the problem ofhigh acoustic attenuation in the skull.

Conventional implementations of communication link relays generally fallinto two categories. The first and most conventional approach is torectify all incoming RF power and use the resulting on-relay DC voltageas a main power source for all communication and control functions ofthe relay, including driving the acoustic transducers of the array. Thisapproach provides maximum design flexibility (e.g., the RF frequency andthe acoustic frequency of the transducers can be the same or they can bedifferent).

The second conventional approach is a more recent approach where theacoustic transducers in the relay are directly driven by the incident RFpower, without any intermediate rectification. This approach sacrificesdesign flexibility for increased efficiency. For example, the RFfrequency and acoustic frequencies need to be the same with thisapproach, but power losses associated with the rectification of thefirst approach are avoided.

Since this design trade-off can be a difficult one in practice, it wouldbe an advance in the art to provide improved hybrid RF-acoustic relays.

SUMMARY

In this work, the above-mentioned problems are mitigated by a powersplitting approach where some of the incident RF power is rectified andused to power the relay, and the remainder of the incident RF power isused to directly drive the acoustic transceivers without beingrectified.

In one example, this approach provides a system and method where RFpower is used to efficiently transfer power across an interface to anRF-to-acoustic relay. The relay converts the RF energy to ultrasonicenergy that powers one or more acoustically powered nodes. In someembodiments, the RF and ultrasonic links can be used for downlink datacommunication, uplink data communication, ultrasonic imaging or anycombination of these functions.

In another example, this approach provides a method and system where RFpower is used to efficiently transfer power across an interface to anRF-to-acoustic relay. The relay converts the RF energy to ultrasonicenergy that powers one or more acoustically powered nodes. Theultrasonic energy can be steered or focused to desired points in space.In some applications, this can be used to power and/or communicate withmultiple acoustically powered nodes. In some embodiments, the RF andultrasonic links can be used to for downlink data communication, uplinkdata communication, ultrasonic imaging or some combination of thesefunctions.

Significant advantages are provided. By splitting incident power in thisway, the power loss associated with rectification can be incurred onlyfor that fraction of the incident power that really needs to berectified, leaving the remaining power free for efficiently directdriving the acoustic transceivers of the relay. Tunable matching to theacoustic transceiver can be done that allows direct driving atselectable frequencies, adding an additional design variable and degreeof freedom. The tuning can also be done in real time to account forchanges in the acoustic transceiver due to varying conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first exemplary system including a first embodiment ofthe invention.

FIG. 2 shows a second exemplary system including a second embodiment ofthe invention.

FIG. 3 schematically shows two approaches for power splitting in ahybrid RF-acoustic relay.

FIG. 4 schematically shows a first implementation approach for phasecontrol in a hybrid RF-acoustic relay.

FIG. 5 schematically shows a second implementation approach for phasecontrol in a hybrid RF-acoustic relay.

FIG. 6 schematically shows a third implementation approach for phasecontrol in a hybrid RF-acoustic relay.

FIG. 7 shows application of principles of this work to a retinal implantsystem.

FIG. 8 shows several exemplary configurations for the ring transceiverof the example of FIG. 7 .

FIG. 9 shows an example of placement of different components of thehybrid RF-acoustic relay in a retinal implant system.

DETAILED DESCRIPTION

FIG. 1 shows a first exemplary system including a first embodiment ofthe invention. Apparatus 120 is configured as a hybrid RF-acoustic relayunit. It includes one or more RF transceivers 106 (individuallyreferenced as 106 a, 106 b, . . . ) configured to receive received RFsignals 112 from an external RF unit 102. Relay 120 also includes one ormore acoustic transceivers 108 (individually referenced as 108 a, 108 b,. . . ) configured to transmit transmitted acoustic signals 114 to oneor more acoustically powered nodes 110 (individually referenced as 110a, 110 b, . . . ). In some embodiments, each acoustically powered node110 may contain one or more acoustic transducer elements. Power forrelay 120 is provided by rectifying some but not all of the incidentpower provided by the received RF signals 112. A remaining part of theincident power provided by the received RF signals is used to directlydrive the one or more acoustic transceivers 108. Here that power splitis shown schematically with rectifier 104 receiving power 118 andremaining power 116 being used to directly drive the acoustictransceivers 108. In this example, the embodiment of the invention isrelay 120.

RF transceivers 106 receive RF power from the external unit or ambientsources. In one embodiment, this may be a coil for inductive powertransfer, an antenna, or an array of coils or antennas. In some forms,it may receive and transmit data. External RF unit 102 provides RFenergy to the RF-acoustic relay. In some embodiments it may alsotransmit data, receive data, or any combination of these. It may includea coil, an antenna, multiple coils and/or antennas. The preferredfrequency range is dependent on the application, but generally carrierfrequencies between 100 kHz to around 15 MHz are used for both the RFand acoustic signals for implant applications. Using direct drive thefrequencies for RF and acoustic signals are the same. The link for datacommunication can use the same frequency, different frequency, the sametransducer element or different transducer elements, or any combinationof these compared to the power signal. Data communication links coulduse different modulation schemes such as amplitude, frequency, and phasemodulation or any combination of these. In a preferred embodiment, thedata received from 112 and the data sent on 114 are amplitude modulatedonto the power signals. Uplink signals such as 206 and 212 on FIG. 2 mayuse multiple input multiple output (MIMO) techniques using multipleacoustic transceivers and/or RF transceivers to maximize the amount ofdata sent. MIMO refers to using multiple acoustic or RF transceivers fortransmitting either from the relay 220 or acoustically powered nodes 110and for receiving either from the relay 220 or acoustically powerednodes 110. Furthermore, the frequencies used for data communication canbe distributed across the above mentioned frequency range. In addition,the transceivers and frequencies used for the two directions of datatransfer to and from the relay can use the same frequency or differentfrequencies. In one implementation when they operate at the samefrequency, the signals are time multiplexed.

Preferably relay 120 is configured such that 60% or less of the incidentpower provided by the received RF signals is rectified to provide powerfor the relay. Preferably this fraction is as low as possible, but manydifferent values are possible depending on the system configuration andthe details of how the overall design is optimized. The rectified powercan be used to drive various DC switch/impedance configurations, as inthe examples shown below, so the minimum dissipated power is due toleakage which depends on the technology used. For example, if thisleakage number is 1 mW for the entire array of acoustic transceivers,then if 100 mW passes through the relay, 1% would need to be rectified;however if 1 W passes through the relay then only 0.1% needs to berectified.

In cases where the link is enhanced with data communication capabilityand/or other functions, additional rectified power will be neededaccording to the power consumed by these extra features. For example, incases where 2-bit or higher phase control of the acoustic transceiversis employed, the required amount of rectified power can be significantlyhigher. E.g., if in the example of FIG. 5 below we assume the 4 switchconfiguration is used to generate 0 and 180 degrees phase and thevariable signal generator 502 generates 90 and 270 degrees phase, thenthe rectified power used for the variable signal generator is on averagearound 50% of the incident power. The additional 10% can account forvariation with different focal points and additional power consumed forother functions (signal processing, data receiver/transmitter circuits,processor, etc.).

The example of FIG. 1 is a unidirectional link to most clearly show thebasic features of embodiments of the invention. In practice it will bepreferred for such links to be bidirectional, and preferably alsoincluding both power transfer and data links. FIG. 2 shows a secondexemplary system including a second embodiment of the invention. Thisexample is like the example of FIG. 1 , except that the hybridRF-acoustic relay 220 includes an on-board processor 202 (typically amulti-input, multi-output processor) powered by power 204 from rectifier104. Here the one or more RF transceivers 106 are also configured totransmit transmitted RF signals 212 to the external RF unit 102.Similarly, the one or more acoustic transceivers 108 are also configuredto receive received acoustic signals 206 from the one or moreacoustically powered nodes 110. Here signals 112, 114, 206 and 212 aretaken to include power, control and data as needed.

Practice of the invention does not depend critically on how the powersplitting between the rectifier and the direct driving is accomplished.Any circuit or system providing this function can be used. FIG. 3schematically shows two exemplary approaches for power splitting in ahybrid RF-acoustic relay. In relay 302 (top half of the figure), asingle RF transceiver 106 provides power to rectifier 104 and toparallel and series impedances (308 and 306 respectively) of each of theacoustic transceivers 108, all in parallel. As is well known, the powersplitting between rectifier 104 and acoustic transceivers 108 will bedetermined according to the impedances of these components, which can beselected to provide the desired power split. In relay 304 (bottom halfof the figure), two RF transceivers 106 a and 106 b are employed thatseparately drive rectifier 104 and transceivers 108, respectively. Herethe power split is determined by how RF transceivers 106 a and 106 b aresized and configured relative to external RF unit 102. In both cases,power from rectifier 104 to control impedances 306, 308 is shown byarrows 316 and 318, respectively. In more complex systems, anycombination of circuit-based power splitting and RF transceiver-basedpower splitting can be used to perform this function including but notlimited to one or more RF transceivers in 102, 106, 106 a, 106 b, etc.

In preferred embodiments of the invention, the acoustic transceivers 108are configured as a phased array of transceivers. FIGS. 4-6 relate tovariations on how this phase control can be performed. Here it isimportant to note that the system architecture of using direct drivingof the acoustic transceivers substantially alters the design of thesephased arrays compared to conventional phased arrays.

More specifically, the conventional way to do beamforming is byrectifying all the power, and using the resulting DC power to driveacoustic transceiver array elements with the desired phase andfrequency. Here that approach is not possible because of the directdriving of the acoustic transceiver array elements.

A major advantage of direct driving of the acoustic transceiver arrayelements is to miniaturize the size of matching circuits. Matchingcircuits are needed to tune out the imaginary impedance of the RFtransceiver and acoustic transceiver elements. At the preferredfrequency range between 100 kHz and 15 MHz for efficient power transfer,the size of capacitors and inductors needed to cancel the imaginaryimpedances of the transceiver elements are large and bulky, limitingminiaturization. By using direct driving, impedances of the acoustictransceivers can be considered to be in parallel so that thecapacitances add into a larger effective capacitance. For thin, flexibletransducers such as PVDF (polyvinylidene fluoride) and P(VDF-TrFE)(polyvinyledenedifluoride-trifluoroethylene), the impedance profile iscapacitive. This allows for a reduction in the required inductanceneeded to cancel the imaginary impedance of the array of capacitivetransducer elements by a factor of the array size squared, potentiallyallowing the imaginary impedance of the RF transceiver to cancel it.

FIG. 4 shows a first beamforming approach. Here RF transceivers 106drive matching circuit 402 which drives acoustic transceivers 108 thatform the array. These transceivers are referenced individually as 410,412, . . . , and details are only shown within transceiver 410. Similardetails are in all the other transceivers, but for simplicity this isnot shown on the figure. The actual transducer element is referenced asT, and can be any acoustic transducer element, e.g., a piezoelectricelement, capacitive micromachined ultrasonic transducer (CMUT), or apiezoelectric micromachined ultrasonic transducer (PMUT). Transducer Tis surrounded by switches S1, S2, S3, S4 connected as shown, whichprovides a 1-bit phase control capability (e.g., 0 degrees, 180 degreesphase shift, or off) as follows.

If switches S1 and S4 are closed and switches S2 and S3 are open, theleft side of T is connected to the top of 402 and the right side of T isconnected to the bottom of 402. If switches S2 and S3 are closed andswitches S1 and S4 are open, the right side of T is connected to the topof 402 and the left side of T is connected to the bottom of 402. Thedifference between these two configurations is a 180 degree phase shift(i.e., 1 bit of phase shift, in digital terms). Additionally the elementcan remained unused by leaving S1-S4 open. Single-bit phased arrays havebeen considered in the RF literature, but are inefficient due to poorbeamforming and lossy switches making it a poor candidate for a powerefficient system. However, for an array of acoustic transceivers and inthis architecture, the high impedance piezoelectric material allows forsmall, low loss switches, making this single-bit approach unexpectedlyattractive. For ultrasonic phased arrays which are primarily used forimaging, the system is not constrained by power consumption or heatdissipation. Therefore rectified DC power would be used to drive thephased array with high resolution phase.

FIG. 4 also shows further features of preferred embodiments of theinvention. More specifically, these features are control block 404,control parameters 406, and control signals 408. Here control parameters406 are inputs to control block 404 that determine how it functions.Most basically, control signals 408 can determine how switches S1, S2,S3, S4 are set for every element in the acoustic transceiver array, toprovide the 1-bit phased array as described above.

However, many further features can be provided with such control and/orin addition to such control. For simplicity, these features are alldescribed here in connection with FIG. 4 , but they should be regardedas applicable to all embodiments of the invention, where possible. Inone embodiment, received data is used to provide control parameters 406.Received data can come from received RF signals 112, received acousticsignals 206, or any combination of the two. In another embodiment,default values are used for control parameters 406.

Various system parameters can be controlled by control parameters 406.Such system parameters include, but are not limited to: RF and acoustictransceiver frequency, the fraction of incident RF power that isrectified, resistance and/or reactance of each acoustic transceiverarray element, parameters of matching circuits 402, and determining whatsystem data is sent as telemetry to external RF unit 102. Such telemetrycan include but is not limited to: the amount of power in the RFtransceivers, the location of the acoustically powered node(s), powerrequirements of the acoustically powered node(s), the number ofacoustically powered node(s), data from the acoustically powerednode(s), impedances of the acoustic transceiver(s), and/or temperatureof the RF-acoustic relay.

In some variations, the external unit may regulate the transmitted powerby using the temperature data from the RF-acoustic relay and/or from theacoustically powered node(s). In other variations, the external unit mayregulate the transmitted power using coefficients of the link strengthbetween the external unit and RF transceivers. One example is the mutualinductance between coils. In other variations, the external unit mayregulate transmitted power using other sensor data on the RF-acousticrelay that may monitor the position(s) of the RF transceivers relativeto the external unit. This can be done using optical sensors and lightemitting structures, and/or additional RF transmitting and receivingstructures. In some variations, the RF-acoustic relay may includeadditional sensors including pressure sensors, optical sensors,temperature sensors, and pH sensors. In other scenarios, the rectifiedpower may be used to send the above mentioned data to adjustcoefficients in additional RF structures placed between the externalunit and RF transceivers such as resonant coils.

To summarize the preceding considerations, control parameters forcontrol of the apparatus can be provided by RF data from the received RFsignals and/or by acoustic data from the received acoustic signals. Thereceived acoustic signals can directly affect the control parameters406. Alternatively, the received acoustic signals can indirectly affectthe control parameters 406 by being transmitted to external RF unit 102which then alters RF signals received by the relay accordingly.

The example of FIG. 5 is similar to the example of FIG. 4 , except thata variable signal generator 502 (analog or digital), which generates asignal with variable amplitude and phase, is provided within each of theacoustic transceivers 510, 512, etc. In other embodiments, 502 may beshared between 1 or more acoustic transceivers (e.g. 510, 512 . . . ).One implementation of the variable signal generator 502 would be using areference frequency signal and rectified power from 104 to drive theacoustic transceiver with controllable amplitude and phase. Thereference frequency signal is used to generate discrete digital phasesand a DAC is used to generate digital amplitude levels, thusimplementing a digital variable signal generator. The referencefrequency signal could include but is not limited to the received RFsignal at the RF transceiver, and a signal generated from a crystaloscillator. Other implementations include but are not limited to usingdelay lines formed from capacitors and inductors to implement an analogvariable signal generator. The frequency of the signal generated from502 can be the same frequency or different frequency than the receivedRF signals. Here in FIG. 5 , a fifth switch S5 is added such that if S3,S5 are closed and S1, S2, S4 are open, the current path throughtransducer T includes variable signal generator 502. In this way, higherresolution phase control can be provided to the acoustic transceiverarray, but more rectified power will be consumed, making it a designtrade-off. The configuration of FIG. 4 can be regarded as having aseries controllable impedance element that includes two or more switchesto control the amplitude and phase. The amplitude can be controlled byvarying the impedance of the switch when closed. In one implementation,this is done by selecting from a bank of differently sized switches tocontrol the impedance, and in another implementation, different voltagelevels are used to drive the switches.

FIG. 6 shows a third approach for controlling the array of acoustictransceivers. In this example, each of the acoustic transceivers 610,612, . . . includes an acoustic transducer T and a series-connectedvariable impedance Z. Individual control of such series impedances(preferably both resistance and reactance) can be used to provide adegree of amplitude and/or phase control for the transceiver array. Therectified DC power can be used to tune the impedances Z of the acoustictransceivers by using switches, capacitors, rectifiers and/or inductors.In one realization, this can be implemented on a silicon chip tominiaturize the system. Such controllable impedances can be analogcontrollable impedances or digital controllable impedances. Analogcontrollable impedances are elements whose impedance vary continuously(e.g. varactor, variable resistor, etc.), and digital controllableimpedances are elements whose impedance only take discrete levels (e.g.switch, switchable bank of impedance elements). This approach canprovide multi-bit amplitude control to improve beamforming capabilityfor direct driving. Using a rectifier in the variable impedance toadjust the current going into each transceiver allows recovery of thisenergy for other uses (calibration, feedback, data transmission etc.).

FIG. 7 shows application of principles of this work to a retinal implantsystem. In this example, the external RF unit 702 includes an RF coil704 and is disposed on a wearable device configured to be worn by thepatient. Glasses are a preferred wearable device for this application.The hybrid RF-acoustic relay 706 can be configured as a contact lens tobe worn on an eye of a patient, and can include an inductive coil 708 toform an RF link with external RF unit 702. Alternatively, the relay canbe configured to be implanted into the lens of the eye of a patient. Aretinal implant 710 can include one or more acoustically powered nodesin acoustic communication with relay 706 as described above. Heretransmitted acoustic signals from relay 706 to implant 710 arereferenced as 712. Similarly, acoustic signals received at relay 706from implant 710 are referenced as 714. For reference, some anatomicalfeatures of the eye are referenced as follows: pupil 716, iris 718,retina 720, and optic nerve 722.

The acoustic transceivers of relay 706 are preferably disposed in a ringsuch that the transmitted acoustic signals substantially do not passthrough the lens of the eye of the patient. FIG. 8 shows severalexemplary ring transceiver configurations for the example of FIG. 7 .Here 802 is an annular transceiver array, 804 is a split array, and 806is a 2D array.

To treat vision loss most effectively, the retinal implant should be inthe back of the eye where cell density is high. When the acoustictransceivers of the relay are placed at the front of the eye, thisfacilitates focusing acoustic power to the retinal implant. A ringstructure will further promote better oxygen perfusion to the eyeallowing for long term usage of the relay 706. Preferred sizes of thearrays 802,804,806 have an inner diameter of about 10 mm to avoidfocusing to the lens of the eye of the patient and to allow oxygen andlight to pass through the cornea. The preferred outer diameter is 18 mmto maximize the aperture size of the contact lens both for acousticfocusing and for the size of the inductive coil 708 on the relay 706.The contact lens may take the form of a scleral lens to accommodate thesize and to increase mechanical stability of the relay 706 in relationto the eye.

In another form, the RF-acoustic relay may be placed outside the side ofthe eye on the sclera next to the skull. The relay can be fixed to aposition on the side of the eye. The RF link can be used to transferpower across the bone and the acoustic transceiver makes good contactwith the eye to efficiently couple energy to the retinal implant. In oneform, the relay also communicates with the implant wirelessly usingultrasound in addition to powering it. In another form, the RF-acousticrelay may be implanted inside the eye under the sclera. In other forms,the RF-acoustic relay may be implanted into the intraocular lens orbehind the lens.

FIG. 9 shows an exemplary placement of different components onto thecontact lens relay 706 for the retinal implant system. The inductivecoil 708 may be implemented by depositing copper or other conductivemetals near the exterior side and towards the periphery of the contactlens such that the outer diameter is similar to the outer diameter ofthe contact lens to maximize coil size. Acoustic transceivers 904 a, 904b, 904 c can be bonded to the contact lens material substrate on theinterior side. Only three acoustic transceivers are shown in FIG. 9 ,but more acoustic transceiver elements such as 8 or 16 elements can beused. In preferred embodiments, the transceivers will cover as much areaon the interior side of the contact lens as possible. Acoustictransceivers elements are preferably spaced closely together to maximizethe aperture; an exemplary spacing is 50 μm. If biocompatible materialsfor the acoustic transducers are used such as PVDF, then the transducerscan be directly exposed to the eye. In other embodiments, matchinglayers can be placed between the transducer and the eye to acousticallymatch. An electronic chip 902 can include various electronic componentssuch as capacitors, inductors and can placed on the contact lenssubstrate towards the exterior side of the contact lens. Chip 902 can beconnected to acoustic transceivers 904 a, 904 b, 904 c, and theinductive coil 708 via metal traces such as copper (traces not shown,for simplicity). All other blocks of the relay 706 such as therectifier, processor, controllable impedance, matching circuits, etc.can be implemented within chip 902 to minimize size and weight. The sizeof the electronic chip 902 may be approximately 3 mm by 3 mm, and theconnections can be made using flip chip technology to minimize footprintof the device and to avoid bond wires to minimize size. In otherembodiments, it can be wire bonded and epoxied to avoid breaking thewires when mounted in the contact lens. In preferred embodiments, theelectronics or the whole contact lens are encased in water-proof softpackaging to extend the longevity of the device.

Due to low acoustic attenuation of the vitreous, carrier wavefrequencies around 10 MHz are preferred for the RF and acoustic signalsin the described retinal implant system. This allows for high focusingefficiency with minimal losses while increasing the bandwidth for datacommunication. In addition, higher frequency of operation allowsminiaturization of required capacitances and inductances used in thematching circuits and of the thickness of the acoustic transducers sincethickness scales roughly inversely with resonant frequency. Flexible,lightweight, and optically transparent materials for the transducers arepreferred to allow more natural light to reach the eye for survivingvision in the patient and to accommodate the shape of the eye. Someexample materials that satisfy these properties are PVDF and PVDFcomposites such as P(VDF-TrFE). These are materials with low thicknessfor a given resonant frequency, low density, flexibility and potentiallyoptically transparency. Specifically at 10 MHz, the thickness at theresonant frequency is around 100 μm which is a suitable thickness for ascleral contact lens. At the thickest portion, the thickness of thetransducer and electronic chip can be less than 300 μm which is stillthinner than normal scleral lenses. The estimated weight of the relayincluding electronics, transducers, RF transceivers, and substratematerial in this embodiment is around 150 mg. Other embodiments withdifferent materials may include non-flexible transducers (e.g. PZT-4,PZT-5, BaTiO₃, PMN-PT (lead magnesium niobate-lead titanate), LiNbO₃)mounted on a flexible substrate.

The invention claimed is:
 1. Apparatus configured as a hybridRF-acoustic relay unit, the apparatus comprising: one or more RFtransceivers configured to receive received RF signals from an externalRF unit; one or more acoustic transceivers configured to transmittransmitted acoustic signals to one or more acoustically powered nodes,wherein each of the one or more acoustic transceivers includes at leastone acoustic transducer; a power splitter configured to split incidentpower provided by the received RF signals into a first part and a secondpart; wherein power for the apparatus is provided by rectifying thefirst part; wherein the second part is used to directly drive the one ormore acoustic transceivers such that an acoustic emission frequency ofthe one or more acoustic transceivers is the same as an RF frequency ofthe second part.
 2. The apparatus of claim 1 wherein the one or more RFtransceivers are configured to transmit transmitted RF signals to theexternal RF unit.
 3. The apparatus of claim 1 wherein the one or moreacoustic transceivers are configured to receive received acousticsignals from the one or more acoustically powered nodes.
 4. Theapparatus of claim 3, wherein control parameters for control of theapparatus are provided by RF data from the received RF signals and/or byacoustic data from the received acoustic signals.
 5. The apparatus ofclaim 1, wherein at least one of the one or more acoustic transceiversincludes a controllable impedance in series with its acoustictransducer.
 6. The apparatus of claim 5, wherein the controllableimpedance is an analog controllable impedance.
 7. The apparatus of claim5, wherein the controllable impedance includes two or more switchesconfigured to provide digital amplitude and/or phase control.
 8. Theapparatus of claim 7, wherein at least one of the one or more acoustictransceivers includes a variable signal generator.
 9. The apparatus ofclaim 8, wherein the variable signal generator is a digital variablesignal generator.
 10. The apparatus of claim 1, wherein controlparameters for control of the apparatus are provided as predetermineddefault parameters.
 11. The apparatus of claim 1, further comprising theexternal RF unit, wherein the external RF unit is disposed on a wearabledevice configured to be worn by the patient.
 12. The apparatus of claim1, wherein the apparatus is configured as a contact lens to be worn onan eye of a patient.
 13. The apparatus of claim 12, wherein the one ormore acoustic transceivers are disposed in a ring such that thetransmitted acoustic signals substantially do not pass through a lens ofthe eye of the patient.
 14. The apparatus of claim 12, furthercomprising the one or more acoustically powered nodes, wherein the oneor more acoustically powered nodes are included in a retinal implant.15. The apparatus of claim 1, wherein the apparatus is configured to beimplanted into a lens of an eye of a patient.
 16. The apparatus of claim1, wherein the power splitter is configured such that the first part is60% or less of the incident power provided by the received RF signals.